There is known in the art a class of devices generally referred to as “scroll” pumps, compressors and expanders, wherein two interfitting spiroidal or involute spiral elements are conjugate to each other and are mounted on separate end plates forming what may be termed as fixed and orbiting scrolls. These elements are interfitted to form line contacts between spiral elements.
A pair of adjacent line contacts and the surfaces of end plates form at least one sealed off pocket. When one scroll, i.e. the orbiting scroll, makes relative orbiting motion, i.e. circular translation, with respect to the other, the line contacts on the spiral walls move along the walls and thus changes the volume of the sealed off pocket. The volume change of the pocket will expand or compress the fluid in the pocket, depending on the direction of the orbiting motion.
Referring to U.S. Pat. No. 6,758,659, a fully compliant, i.e. axially and radially, “floating” scroll mechanism with dual-scroll structure is disclosed. Referring to FIG. 1, the dual orbiting scrolls have spiral vanes on opposite sides of the end plates. In a floating scroll, the orbiting scroll is dynamically well balanced, axially and radially. The scrolls are fully, i.e. axially and radially, compliant for maintaining minimum contacting forces between components, hence achieving good sealing for high speed, high efficiency, low friction wear and power loss. A central crank shaft-sliding knuckle and/or peripheral cantilever crank pin-sliding knuckle mechanism provide the dual orbiting scroll with radial compliant capability. A synchronizer is used to synchronize the orientation of the crank handles to prevent the mechanism from jamming during operation and start up.
However, a very small relative sliding motion, or excursion, exists between the peripheral crank pin and sliding knuckles. This excursion can cause fast wear of the parts in oil-free environment. Besides, the friction wear and friction power loss resulting from axial thrust forces in a floating scroll device, particularly when the pressure differential between the discharge gas and the suction gas is large, needs to be further reduced to improve the energy efficiency and durability.
U.S. Pat. No. 4,160,629 to William P. Hidden et al. discloses non-traditional thrust ball bearings to utilize the rolling effects of balls to bear thrust forces. In non-traditional thrust ball bearings, the balls circle locally at an orbiting radius and thus, the life of the bearing is reduced. In addition, a non-traditional thrust bearing is technically complicated and costly to produce.